The present invention is directed to methods of fabrication of electrically conducting polymers having enhanced electrical conductivity. In particular, the present invention is directed to methods to deaggregate electrically conductive and precursors thereof.
Electrically conductive organic polymers have been scientific and technological interest since the late 1970""s. These relatively new materials exhibit the electronic and magnetic properties characteristic of metals while retaining the physical and mechanical properties associated with conventional organic polymers. Herein we describe electrically conducting polyparaphenylene vinylenes, polyparaphenylenes, polyanilines, polythiophenes, polyazines, polyfuranes, polypyrroles, polyselenophenes, poly-p-phenylene sulfides, polyacetylenes formed from soluble precursors, combinations thereof and blends thereof with other polymers and copolymers of the monomers thereof. In order for these materials to be used in place of metals in more applications, it is desirable to increase the conductivity of these materials.
The article xe2x80x9cThe Concept of Secondary Doping as Applied to Polyanilinexe2x80x9d, A. G. MacDiarmid, A. J. Epstein, Synthetic Metals, 65 (1994), 103-116, describes increasing the electrical conductivity of a polyaniline by exposing a doped polyaniline to a secondary dopant, such as meta-cresol. MacDiarmid et al. teaches that the secondary dopant results in an intra-molecular conformational change in the polyaniline molecule. Prior to being exposed to the secondary dopant, the doped polyaniline molecule is in a compact coil intra-molecular conformation. Intra-molecular conformation refers to the conformation of a single molecule or a single polymer chain in which the molecular chain is coiled around itself. In contra-distinction inter-molecular structure refers to the structural arrangement of more than one molecule or polymer chain in which the molecules or chains are bonded together or coiled around each other forming aggregates. These aggregates are then comprised of many polymer chains intertwined or entangled. MacDiarmid et al. teaches that the secondary dopant causes a intra-molecular conformational change, i.e., the molecule or the chain unravels and assumes an expanded coil conformation. A film of this expanded coil polyaniline has enhanced electrical conductivity because of an increase in the crystallinity of the material formed from the aggregated straightened molecules.
In the article xe2x80x9cTransport studies of protonated emeraldine powder: A granular polymeric metal systemxe2x80x9d, F. Zuo et al., Phys. Rev. B 36, 3475 (1987) it has been reported that the polyaniline which has been doped has electrically conductive regions or islands which are of the order of 200-300 xc3x85. The spaces between these regions are significantly less electrically conductive. When an electrical current flows along the polyaniline molecules, current flows through the electrically conductive regions and hops over the less electrically conductive region to an adjacent electrically conductive region.
It is an object of the present invention to increase the electrical conductivity of electrically conductive polymers.
It is another object of the present invention to enhance the electrical conductivity of an electrically conductive polymer by deaggregating aggregated molecules which are precursors of the electrically conducting polymers so that the molecules can be more uniformly doped.
It is another object of the present invention to deaggregate polymer molecules prior to being doped to the electrically conducting state.
It is another object of the present invention to lower the glass transition temperature of the precursor to an electrically conductive polymer and of an electrically conductive polymer by the addition of deaggregating agents.
It is another object of the present invention to increase the electrical conductivity of electrically conductive polymers by extending the electrically conductive regions or islands of the electrically conductive polymer.
It is another object of the present invention to further increase the electrical conductivity of a deaggregated electrically conductive polymer by stretch orientation.
It is another object of the present invention to increase the shelf-life of a precursor to an electrically conductive polymer and of an electrically conductive polymer by the addition of deaggregating agents.
A broad aspect of the present invention is a method for fabricating electrically conducting polymers, the electrical conductivity of which is enhanced by deaggregating the polymer either prior to being doped to the electrically conducting state or after being doped to the electrically conducting state.
A more specific aspect of a method of the present invention is deaggregating the precursor polymer or electrically conducting polymer either in solution or in the solid state, such as by using complexing agents.
Another more specific aspect of a method of the present invention includes steps of providing a first admixture of an additive in a solvent; forming a second admixture by dissolving in the first admixture precursor polymers to electrically conducting polymers wherein the additive deaggregates the precursor molecules and either adding a dopant to the second admixture to dope the precursor to the electrically conductive polymer or forming a film of the second admixture and then doping the film in the solid state.
Another more specific aspect of a method of the present invention includes providing aniline molecules which are oxidatively polymerized in an acid solution in the presence of a deaggregating agent to result in a deaggregated polyaniline.
Another more specific aspect of a method of the present invention includes the steps of providing aniline molecules which are oxidatively polymerized in an acid solution to form an electrically conducting polyaniline salt which is then neutralized to the base non-doped form and deaggregated upon exposure to a deaggregating agent.
Another more specific aspect of a method according to the present invention includes neutralizing a polyaniline salt to the base form in the presence of a deaggregating agent.
Another broad aspect of the present invention is a method of causing a doped electrically conductive polymer in a compact coil conformation to undergo a conformational change from a compact coil to an expanded coil conformation by exposing the doped polymer to salts and surfactants.